The present invention relates to a surface acoustic wave device which is suited, for example, to a transceiver or a transmitter and a receiver for mobile communications such as cellular radio.
A conventional surface acoustic wave filter comprises an input or output interdigital transducer mounted on a piezoelectric substrate for converting an electric signal to a surface acoustic wave or a surface acoustic wave to an electric signal and an intermediate interdigital transducer for connecting inputs when necessary. Such a surface acoustic wave filter is described, for example, in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-33, No. 6, pp. 510-518, June 1985.
In the prior art, assuming that a wavelength of a surface acoustic wave propagating at a frequency equivalent to the center frequency (frequency at the center of the pass band) of the filter is .lambda.o, width of each of interdigital electrode fingers is about 1/4 of the wavelength or .lambda.o/4. The value of .lambda.o is proportional to the reciprocal of the center frequency of the surface acoustic wave filter; that is, the value of .lambda.o decreases as the frequency increases. When the frequency is 1 GHz, for example, the value of .lambda.o is about 5 .mu.m, and the electrode finger width becomes 1.0 to 1.25 .mu.m.